Assistance systems may be used with steering device of vehicles, such as motor vehicles. Assistance systems may range from, for example, power steering systems to independently acting steering systems for use in parking situations. For instance, support systems and assistance systems for the steering devices of vehicles, especially of motor vehicles, range from almost fully established power steering to automatic active steering systems, e.g. in parking situations. Such systems increasingly intervene actively in the steering process, even while travelling, in order to increase the ride comfort and safety for the occupants.
Power steering systems differ in the form of their drive. Hydraulically (HPS=“Hydraulic Power Steering”) and electrohydraulically (EHPS=“Electro-Hydraulic Power Steering”) supported steering systems generally boost the manual steering wheel torque applied by a driver to enable a more comfortable steering function. Electromechanically supported steering systems (EPAS=“Electro Power Assisted Steering”) actively apply steering torques to exert assistance functions and to assist the driver in his control of the vehicle.
Conventional assistance systems may be used to facilitate maintaining the straight running of the vehicle for a person steering the vehicle. Such systems reduce the work required by a driver and support the driver in relation to the force to be exerted to control of a vehicle during travel. However, changing external influences place high demands on such systems, requiring continuously adapted and complementary interaction of actions and reactions by the driver and the assistance systems. Thus, particularly for vehicles with an EPAS system, demands may be placed upon a driver during normal straight running conditions if no additional automatic correction is performed to compensate the pulling action and drift (PDC=“Pull Drift Compensation”) that may occur.
As used herein, a pulling action (steering pull) requires a noticeable force to be applied to a steering wheel to enable straight running. As used herein, drift means the readiness of the vehicle to deviate from the straight direction of travel during hands-free travel by a driver. The driver is forced to apply a constant counter steering torque, via the steering wheel, when traveling on humped roads with lateral cambers and/or a road having a generally steep slope. Further, vehicle geometry misalignments, such as camber/caster split angle, toe angle, tire aligning torque, may influence the straight running of a motor vehicle, while requiring a constant counter steering torque to be applied by the driver. In order to reduce such efforts, appropriate PDC systems have been incorporated as a feature in modern EPAS systems.
In principle, a distinction is to be made between long-term and short-term corrections regarding the torques to be applied by the driver or the respective system. Long-term corrections relate to unavoidable effects intrinsic to the vehicle, such as a faulty or deteriorating vehicle setting. These effects can result, for example, from different tire air pressures or a displacement of the steering geometry. Short-term corrections are caused by external influences, such as, for example, a suddenly occurring side wind, a road camber, or the gradient of a road. These influences can affect the driving dynamics and lead to vehicle drift.
Conventional methods and systems for PDC support have already contributed to a significant improvement in safety and comfort. However, these methods and systems are not suitable for compensating necessary corrections due to vehicle design settings. Thus, these methods and systems cannot be used, for example, to check whether any wheels are positioned incorrectly and to make corresponding corrections. Nevertheless, newly manufactured vehicles may exhibit vehicle design settings that lead to compensations for straight running of a vehicle, such as due to manufacturing tolerances.